Models in Irrigation andWater Management - Practices of Irrigation and On-farm Water Management - page 380

Relevant Journals ................................ 419
Questions .................................... 419
References ................................... 420
In some cases, we need to know the knowledge of specific process within a complex
system of interacting and interdependent phenomena, and then need to reintegrate
such knowledge to obtain a comprehensive and accurate solution of the phenomena.
Model is ideal to integrate the complex system and to obtain the answer if the con-
dition is. It is merely a useful tool in obtaining answers in the choice of a decision
or policy.
By definition, model is a simplified representation of reality. It may be a system
of equations that shows how parameters and variables of interest are related to one
another. A model can come in many shapes, sizes, and styles. Models of different
types are discussed in this chapter. Different issues of modeling aspects such as
calibration, sensitivity analysis, validation have been described. Different up-to-date
statistical indicators for model performance evaluation have been discussed, and
overview of some of the commonly used models is included. In addition, utility of
crop production functions along with their development techniques/philosophy is
described. And finally, development procedure of regressed-based empirical crop
prediction model from weather variables is explained with sample data.
10.1 Background/Need of a Model
One of the main factors for the intensification of the agricultural production of
plants is irrigation. In order to get the optimal results, it is necessary to calculate
the required quantity of water in dependence of some parameters, for example of
the environment, the subsurface geo-hydrological condition, type of crop, the stage
of the growth, and growth rate. Some of the fundamental problems of agricultural
and environmental research are how to obtain knowledge of specific process within
a complex system of interacting and interdependent phenomena, and then how to
reintegrate such knowledge so as to obtain a comprehensive and accurate solution
of the phenomena. Model is ideal to integrate the complex system and to obtain the
answer if the condition is.
Crop growth simulations are needed to help organize our knowledge of plant
response to the environment for the purpose of assisting growers in management
decisions, predicting impacts of land use decisions, and predicting the consequences
of probable climatic variations.
10.2 Basics of Model: General Concepts, Types, Formulation
and Evaluation System
10.2.1 General Concepts
A model is merely a useful tool in obtaining answers in the choice of a decision or
policy. It may be a system of equations that show how parameters and variables of